Magnetically driven formation of 3D freestanding soft bioscaffolds

3D soft bioscaffolds have great promise in tissue engineering, biohybrid robotics, and organ-on-a-chip engineering applications. Though emerging three-dimensional (3D) printing techniques offer versatility for assembling soft biomaterials, challenges persist in overcoming the deformation or collapse of delicate 3D structures during fabrication, especially for overhanging or thin features. This study introduces a magnet-assisted fabrication strategy that uses a magnetic field to trigger shape morphing and provide remote temporary support, enabling the straightforward creation of soft bioscaffolds with overhangs and thin-walled structures in 3D. We demonstrate the versatility and effectiveness of our strategy through the fabrication of bioscaffolds that replicate the complex 3D topology of branching vascular systems. Furthermore, we engineered hydrogel-based bioscaffolds to support biohybrid soft actuators capable of walking motion triggered by cardiomyocytes. This approach opens new possibilities for shaping hydrogel materials into complex 3D morphologies, which will further empower a broad range of biomedical applications.


Fig. S7. Effect of CaCO3 and iron oxide powders on cell viability tested using Human Umbilical Vein Endothelial Cells (HUVECs). (A)
Scheme showing the three groups being tested for each powder."no exposure" is a control group, "2 h exposure" is the group with powders kept with cells for 2 hours and then removed, and "Long term exposure" is the group with powders kept with the cells for 7 days.

Fig. S3 .
Fig. S3.The effect of temperature on the material property and the 3D transformation of the different patterns.(A) Storage (G′) and loss (G″) moduli of 20% (w/v) gelatin during temperature sweep (from 7 °C to 37 °C).(B) Schematics of the molded flat hydrogel precursors, and the photos of their 3D transformation when at (C) 25 °C and (D) 30 °C.(Scale bars: 1 cm).

Fig. S4 .
Fig. S4.Fabrication of GelMA scaffolds with 3D branching vascular channels by magnetically driven transformation.(A) Molded flat sacrificial hydrogel precursors; (B) magnetically driven transformation of the sacrificial hydrogel precursor into 3D morphology followed by UV crosslinking of the GelMA bath; (C) crosslinked bath material (GelMA) with embedded sacrificial 3D branching hydrogels, which can be sacrificed when placed into 37°C incubator to generate bioscaffolds with 3D branching vascular channels; (D) perfusion of blue dye solution into the 3D branching vascular channels; (E) different views of a perfused bioscaffold with 3D branching vascular channels.(Scale bars: 10 cm).

Fig. S5 .
Fig. S5.Fabrication of collagen bioscaffolds with 3D branching channels by magnetically driven transformation.(A) Time-lapse images showing the crosslinking process of the collagen bath at room temperature.(B) Perfusion of blue dye solution into the 3D branching channels within crosslinked collagen after gelatin removal.(Scale bars: 1 cm).
Fig. S7.Effect of CaCO3 and iron oxide powders on cell viability tested using Human Umbilical Vein Endothelial Cells (HUVECs).(A) Scheme showing the three groups being tested for each powder."no exposure" is a control group, "2 h exposure" is the group with powders kept with cells for 2 hours and then removed, and "Long term exposure" is the group with powders kept with the cells for 7 days.(B) The effect of CaCO3 powders on HUVECs viability.(C) The effect of iron oxide powders on HUVECs viability.(Data are shown as average ± s.d., n = 6 from one experiment.*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001 based on two-way ANOVA test.).

Fig. S8 .
Fig. S8.Magnet aided removal of magnetic ink containing iron oxide particles.The crosslinked bath material with embedded sacrificial 3D branching hydrogels (A) before and (B) after incubation at 37° C. (Scale bars: 1 cm).

Fig. S13 .
Fig. S13.HUVECs and NHLFs within fibrin during fibrin crosslinking at room temperature.HUVECs were coloured with CellTracker TM Green CMFDA and mixed in gelatin precursor before fabricating the fibrin scaffold.NHLFs were coloured with CellTracker TM Orange CMRA and mixed with fibrin matrix before the fabrication.(A) Fluorescent image of 488 nm channel.Green signal indicates the presence of HUVECs.(B) Fluorescent image of 555 nm channel.Orange signal indicates the presence of NHLFs.(C) Merged image of both channels.(Scale bars: 200 µm).